Field of the Invention
The present invention relates to an image processing technology for calculating a defocus amount that is a difference between an imaging plane of an image capturing optical system and an imaging plane in an image capturing apparatus.
Description of the Related Art
An image capturing apparatus, such as a digital still camera, acquires a plurality of parallax images having parallaxes by capturing an object at mutually different viewpoints, and calculates a defocus amount using the parallaxes among the plurality of parallax images.
Japanese Patent Laid-Open No. (“JP”) 2001-083407 discloses an image capturing apparatus that includes an image sensor in which each of a plurality of pixels has one micro lens and a plurality of (two) photoelectric converters, and the plurality of photoelectric converters in each pixel are configured to receive light fluxes that have passed different areas in a pupil in an image capturing optical system. This image capturing apparatus calculates an image shift amount (phase difference) between a pair of signals obtained from the two photoelectric converters in each of the plurality of pixels, and calculates a defocus amount based on the image shift amount. The image capturing apparatus disclosed in JP 2001-083407 reads signals separately from the two photoelectric converters for each pixel, and needs a time period to read the signal for one pixel twice as long as that required to read the signal from one photoelectric converter.
JP 2013-068759 discloses an image capturing apparatus that can provide addition reading and independent reading of the signals from two photoelectric converters in each pixel. This image capturing apparatus acquires a pair of signals by independently reading a signal from each of the two photoelectric converters only for in pixels arranged at a predetermined arrangement period in calculating the image shift amount between the pair of signals. This configuration can calculate an image shift amount while restraining a signal readout time period from increasing. In addition, the image capturing apparatus disclosed in JP 2013-068759 obtains a pair of signals having a resolution higher than that of the independent reading in each frame by changing the independent reading pixel row for each frame in motion image capturing.
However, JP 2013-068759 is silent about the way of calculating the image shift amount or the defocus amount using the pair of image signals obtained by changing the independent reading pixel row for each frame in the motion image capturing. In addition, the image capturing apparatus disclosed in JP 2013-068759 may calculate the defocus amount less precisely as in capturing the moving object or in hand vibrations in hand-held image capturing.